In current wireless broadband standards such as Third Generation Partnership Project Long Term Evolution (3GPP LTE), the control channel capacity usually is highly limited. Specifically, there may be about 10 Physical Downlink Control Channel (PDCCH) signaling which can be sent in one Transmission Time Interval (TTI) in a 10 MHz system bandwidth scenario, in which about at most 10 User Equipments (UEs) can be scheduled for either Downlink (DL) or Uplink (UL) data transmission. While dedicated UEs need to follow scheduling information carried by PDCCH, in fact a large proportion of Control Channel Elements (CCEs) has to be used for non-dedicated/common functions. For instance, about a total of 41 CCEs is available when 3 OFDM symbols are allocated for PDCCH, but out of the 41 available CCEs, up to 16 Control Channel Elements (CCEs) are commonly allocated for Common Search Space (CSS) including control functionalities such as System Information (SI), Paging, Random Access (RA), Transmission Power Control (TPC), and so like. This leaves only about 25 CCEs available for dedicated UE scheduling. For another example, in a scenario where 2 OFDM symbols are allocated for PDCCH, only about 10 CCEs out of a total of 25 CCEs are available for dedicated UE scheduling.
However, the channel capacity is further limited under the circumstance of Carrier Aggregation (CA). In Carrier Aggregation (CA), cross-carrier scheduling may be used to schedule resources on another serving cell and therefore reduce inter-cell interference in Heterogeneous Networks. In addition, cross carrier scheduling may be used to schedule resources on non-backward compatible carriers. For instance, when a wireless communication system is operating with extension carriers, during a sub-frame in which the allocated frequency band for a first carrier (CC1) may contain data in the Physical Downlink Shared Channel (PDSCH) and a second carrier (CC2) may contain data in its PDSCH, the control region of a first carrier (CC1) may actually contain PDCCH for both CC1 and CC2 while no PDCCH or Physical Hybrid ARQ Indicator Channel (PHICH) or Physical Control Format Indicator Channel (PCFICH) would exist in the control region of CC2 in order to avoid interference to control region of other cells. For another example of non-backward compatible carriers, the control region for the single carrier may contain control signaling for both backward and non-backward compatible PDSCH regions, while the control region for a neighboring PDSCH is suppressed in order to avoid interference to control regions of other cells. This means that using carrier aggregation would further limit control channel capacity.
In a practical scenario, for example, the applications of instant communications (e.g. messages services and social networks) have long packet inter-arrival time while intermittent transmission of small amounts of data is used. In additional, the time of arrivals between packets may be large. If a scheme of periodic resource allocation is adopted, it would result in a waste of resource allocation if the scheduled period were short but would otherwise adversely affect interactivity if the period were long. For real time services such as gaming, video surveillance, remote control, and so like, tight delay and frequency transmissions of small amounts of data having variable sizes. Also for machine type of communication in general, such as machine-to-machine traffic, a large amount of small data traffic with variable sizes is required. Therefore, all that has been described necessitate a need for a mechanism to reduce the control signal (e.g. PDCCH) overhead.
Semi-Persistent Scheduling (SPS) could be used to reduce the control signal overhead. For services involving a semi-static packet rate such as VoIP, SPS can be configured to reduce the control signal overhead. For this kind of service to be implemented, the timing and the amount of radio resources require predictability. The SPS enables radio resources to be semi-statically configured and allocated to a UE for a longer time period than one sub-frame, and the SPS may avoid the need for transmitting specific downlink assignment messages or uplink grant messages over the PDCCH for each sub-frame. However, the SPS may not be suitable for other Internet applications such as social network applications since updating information on the social network website could not be easily predicted.